GEOLOGY, RELIEF AND DRAINAGE

Keuper Marl, a plastic red clay some hundreds of feet deep in level beds, covers the whole of Bordesley and Deritend A relatively thin layer of sandy and gravelly drift overlies the central third of the area and provides the relief. (Two embayments in the northern edge of the drift shown on the O.S. Drift Geology sheet are due to quarrying). The highest point of the Bordesley plateau is 435 feet, at Blake Lane/Yardley Green Road corner. There is a small drift patch on Hobmoor Road. Alluvium floors the valleys of the Rea (3-400 yards wide), Cole (2-300 yards), and Hol Brook (70 yards). A number of streams used to flow radially from the drift cap reservoir of central Bordesley.

The swollen torrents of post-glacial times of which yesterday's trickles were the descendants washed drift from lower areas. Very gentle declines on the plateau's east and south sides contrast with relatively steep slopes into the Rea valley, where the volume of melt-water and thence the degree of wear were greater. Clay is waterbound and impermeable: surface water remains in the topsoil, producing a natural cover of thick oak forest and impenetrable undergrowth.

At boggy valley edges and on stony drift the oaks thin out. Thus the water borders of Deritend and Bordesley would be lush marshy meadows fringed by willows, forest would cover the flatlands and climb the slopes, but the plateau would bear lighter wood, birch and hazel predominating, except where the soil was so sandy and gravelly that it bore only gorse, broom, and grass.

Few names have survived to confirm the ancient vegetation cover. Heath Mill stood at the drift edge. On John Tomlinson's map of 1760, first to give useful detail, are found Stony Croft on Garrison Lane, Gorsty Meadow (Arthur Street south), and Gorsty Leasow (Bankes/Floyer Roads, west ends). 'Golden Hillock', later, was golden with broom and gorse. Then there are Broom Lea (Glovers/Langley Roads), Birch Field (Hickman Road), Rushy Piece in the valley of Little Hay Brook, Hob and Slanch Moors (bogs). Small Heath was on drift. Great Wood (east from Muntz Street) a copse on a clay embayment where Hol Brook (holm, water-meadow) has washed away the gravel, another at Kingscliff/Edsbrooke Roads, and a spinney by Yardley Green Hospital, are the only reminders of Bordesley Wood.

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